A reward poster is displayed on the entrance to the 40th St-Lowry St Station, where a man was killed after being pushed onto the subway tracks, in the Queens section of New York, Friday, Dec. 28, 2012. Police are searching for a woman suspected of pushing the man and released surveillance video Friday of her running away from the station. (AP Photo/Seth Wenig)

For New York City, it wasn't an unusual sight: a possibly mentally ill woman pacing and mumbling to herself on an elevated subway station platform.

The woman eventually took a seat on a bench Thursday night, witnesses later said. Then, without any warning or provocation, she sprang up and used both hands to shove a man into the path of an oncoming train.

As police sought on Friday to locate the unidentified woman, Mayor Michael Bloomberg urged residents to keep the second fatal subway shove in the city this month in perspective. The news of the horrific death of 46-year-old Sunando Sen, who was from India and lived in Queens, came as the mayor touted drops in the city's annual homicide and shooting totals.

"It's a very tragic case, but what we want to focus on today is the overall safety in New York," Bloomberg told reporters following a police academy graduation.

The New York Police Department released a sketch of the woman and surveillance video of her fleeing the area and interviewed witnesses, including some who described her as acting agitated before the attack.

Some witnesses said Sen had been shielding himself from the cold by waiting in a stairwell before he ventured out onto the platform to see if the train was coming. They also said he had no interaction with the woman, who immediately darted down a stairway after she pushed him.

One witness told police that Sen had no time to try to save himself. The witness turned away to avoid seeing him getting crushed on the tracks.